1. Field of Invention
This invention relates to a method and apparatus for stretching plastic material, and, more particularly, to a method and apparatus for stretching dough for bread or confectionery.
2. Description of Prior Art
Plastic materials or dough for bread or confectionery have been continuously stretched by various types of stretchers.
U.S. Pat. No. 4,192,636 discloses an apparatus for stretching dough in which a plurality of serially disposed conveyors, each being driven at a different speed, is arranged. A roller mechanism is disposed above these conveyors. It comprises a plurality of rollers that are freely rotatable about their axes. They constitute an endless elliptical path having a straight part spaced apart from and located over the serially disposed part of the conveyors. Also, U.S. Pat. No. 4,692,110 discloses an apparatus for stretching dough in which a plurality of conveyors, each being driven at a different speed, are serially disposed. In it a roller mechanism, comprising a plurality of rollers that are freely rotatable about their axes, and that constitute a straight path, are spaced apart from and located over the serially disposed portion of the conveyors. Since in these prior apparatuses the conveying speed of the downstream conveyor is higher than that of the upstream conveyor, and the dough being conveyed by the serially disposed conveyors is gently held by the rollers that are advancing downstream or reciprocating over the surface of the dough, it is smoothly stretched.
However, the roller mechanism has a heavy and complex structure, so that it requires high production, maintenance, and repair costs. Therefore, an apparatus for stretching dough that is simple, functions steadily, and that has low production costs, has been desired.
Therefore, this invention provides a method and apparatus for stretching dough in which two serially disposed conveyors, and a roller that is rotatable about its axis and that is reciprocated over a downstream conveyor, are arranged. According to this invention dough is first stretched by the effect of the different speeds of the two conveyors. It first becomes dough with a roughly stretched and uneven surface. The surface of this roughly stretched dough is then made smooth and further stretched by the rotation of the roller on the surface of the dough. Thus, the dough can be smoothly stretched by the apparatus of this invention, as in the prior art apparatuses.
It has been accepted that to stretch dough that has a height (H) to produce a dough strip that would have the same thickness as the distance (D) between the roller and the conveying surface of the downstream conveyor, the following formula should be met in the stretching operation: EQU V.sub.1 /V.sub.2 =D/H
wherein (V.sub.1) represents the conveying speed of the upstream conveyor, and (V.sub.2) represents the conveying speed of the downstream conveyor.
According to the apparatus of this invention, dough is effectively stretched when the above formula is met.
Since in this invention only a means for reciprocating the roller is provided, other than the roller and a pair of conveyors, the structure of the apparatus is simple.
It is therefore an object of this invention to provide a method of stretching dough in which a roller is reciprocated over the surface of the dough being continuously conveyed by a downstream conveyor that is disposed serially with an upstream conveyor, while the roller is rotated on the surface of the dough. The dough is first stretched when it is transferred from the upstream conveyor to the downstream conveyor, and then the roughly stretched dough, which has a smooth surface, is further stretched by the roller located above the downstream conveyor. Since the dough being conveyed by the downstream conveyor is uniformly compressed by the roller that is repeatedly reciprocating over the surface of the dough, the gluten tissue of the dough does not suffer any excessive compression from the roller, and thus the dough is effectively and uniformly stretched.
Another object of this invention is to provide an apparatus for working the above-mentioned method. It comprises an upstream conveyor, a downstream conveyor that is disposed serially with the upstream conveyor, the conveying speed of said downstream conveyor being higher than that of the upstream conveyor, a roller rotatable about its axis and located above the downstream conveyor, and means for reciprocating the roller by a predetermined distance (1) along a moving path spaced apart from the conveying surface of the downstream conveyor. Since the apparatus of this invention only requires means for reciprocating the roller, other than a roller and a pair of conveyors, the structure of the apparatus is simple. This leads to low production costs in making the structure.